1. Field of the Invention
The present invention relates to a variable geometry cylinder mirror and more particularly to a highly configurable, high precision cylindrically deformable variable geometry mirror.
2. Description of the Related Art
In the field of high-precision micro optical systems such as an optical pickup, a micro variable focus mirror capable of changing the curvature of its reflecting face has been proposed so as to aim at simplification of the structure for focusing, which conventionally uses an electromagnetic actuator.
Further, in a small image pickup optical system, miniaturization is largely dependant on the size of the variable focus mirror.
Adoption of micro electromechanical system (MEMS) technology in a variable focus mirror enables low-cost, high-precision manufacturing thereof.
An example of the cylindrically deformable variable geometry cylinder mirror of this technology is a monolithic reflecting mirror apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
In this monolithic reflection mirror unit, as shown in FIG. 26, a metallic thin film 54, which serves as an electrode layer, is formed on a silicon semiconductor substrate 51, which acts as a fixed side electrode, through a silicon epitaxial layer 52 and a silicon oxide thin film 53. Window holes 56, 57 are formed in the silicon oxide thin film 53 and the metallic thin film 54 with a central portion 55 left between them.
Because the window holes 56, 57 communicate with each other through a vacant portion 58 formed in the silicon epitaxial layer 52, the central portion 55 is set up as a straddle-mounted type reflection mirror portion.
The straddle-mounted type reflection mirror portion 55 opposes the silicon semiconductor substrate 51 through the vacant portion 58. By applying a potential difference to 51 and 55, the reflection mirror portion 55 is distorted, thereby functioning as a variable geometry cylinder mirror.
However, although the variable geometry cylinder mirror employing the conventional monolithic type reflection mirror unit can be so constructed as a small, low-cost variable geometry cylinder mirror, the electrostatic force applied to the reflection mirror portion cannot be changed according to each position. Thus, this variable geometry cylinder mirror cannot be deformed to an asymmetrical shape.
Further, the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit can only be changed from a flat face to a concave face and it cannot be deformed to a convex shape.
Additionally, because the center of the reflection mirror portion always drops with deformation of the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit, there is a problem that the curvature cannot be changed with the center portion fixed.
Further, the straddle mounted type structure is distorted by deformation of the reflection mirror portion. Thus, if a large distortion is desired, a high voltage is needed in order to produce a large electrostatic force.